Our long term goal is to understand how sex steroids regulate G protein-coupled receptor mediated neurotransmission that underlies hormonal activation of behavior. We have demonstrated that estrogen activation of [unreadable]-opioid receptors (MORs) is necessary for the full display of sexual receptivity. The neural circuit that regulates this behavior involves the hypothalamic arcuate nucleus (ARH) and the medial preoptic nucleus (MPN) and requires the activation of estrogen receptor-a (ERa), neuropeptide Y (NPY)-Y1 receptors and release of [unreadable]-endorphin ([unreadable]-END). Preliminary studies indicate that metabotropic glutamate receptors (mGluR) are involved in estrogen-induced MOR internalization/activation in the MPN and the regulation of lordosis. The present proposal will examine signaling mechanisms through which estrogen activates this ARH-MPN pathway. The general hypothesis tested is that estrogen activation of MOR in the MPN depends on membrane associated ERa interactions with mGluR1a and GABA-B receptors in the ARH. The ER- mGluR interaction mediates GABA-B receptor function, uncoupling the receptor from a G protein-gated inward rectifying potassium (GIRK) channel. The proposal is divided into three Specific Aims: 1. Estrogen-induced MOR internalization in the MPN is due to an interaction of membrane associated ERa with mGluR1a to block GABA-B receptor inhibition of NPY neurons. This is tested through a series of pharmacological studies that systematically block or activate these receptors. 2. ERa, mGluR1a and GABA-B receptors are expressed by NPY neurons in the ARH. Immunohistochemical studies will determine the co-localization of these receptors and co-immunoprecipitation will determine if ERa directly interacts with mGluR1a. To determine the mechanism of estrogen-induced NPY expression, real time RT-PCR will be used to measure the effects of estrogen signaling through the mGluR on NPY mRNA expression. 3. Estrogen-induced lordosis depends on the sequential activation of ERa, mGluR1a and inhibition of GABA-B receptors. Behavioral experiments will test the how activating membrane associated ER and mGluR affect intracellular signaling pathways regulating lordosis. Estrogen is an important but not well understood neuroactive substance. The results from these studies will help design appropriate estrogen therapies to rescue reproductive, feeding and cognitive dysfunctions that rely on estrogen signaling in the brain.